GATE Notes,

Probability Formulas

Probability Range

0 ≤ P(A) ≤ 1

Rule of Complementary Events

P(A

^{c}) + P(A) = 1
Rule of Addition

P(A∪B) = P(A) + P(B) - P(A∩B)

Disjoint Events

Events A and B are disjoint iff

P(A∩B) = 0

Independent Events

Events A and B are independent iff

P(A∩B) = P(A) ⋅ P(B)

Conditional Probability

P(A | B) = P(A∩B) / P(B)